For city cyclists, weaving in and out of traffic as they snake their way through the urban jungle can make them feel invincible.

But there are fears that while traditional bike helmets can make cyclists take more risks, they do not offer sufficient protection to prevent injuries.

Now researchers in the US believe an alternative to the hard foam helmets borrowed from the airbags found in most modern cars could help to save lives - but need Congress to allow them to go on sale in America.

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Airbag 'helmets' are already commercially available from companies like Hövding (pictured). The airbag is contained in a collar that features algorithms that detect sudden movements of the head in a crash and deploy the airbag in a fraction of a second

BANNED IN AMERICA

These inflatable helmets cannot be sold in the United States due to current federal regulations.

U.S. regulations do not reflect new research on the dangers of concussions and other brain injuries, researchers say.

The Consumer Product Safety Commission, which regulates bicycle helmets, does not even have a testing method in place for inflatable versions, he added.

These inflatable helmets cannot be sold in the United States due to current federal regulations.

A team at Stanford University is crash testing the helmets to measure the level of protection they provide against standard foam helmets.

While traditional helmets can make the difference in a crash, reducing skull fractures, riders may not be as safe as the think they are.

'Foam bike helmets can and have been proven to reduce the likelihood of skull fracture and other, more severe brain injury,' said David Camarillo, a bioengineer at Stanford.

'But, I think many falsely believe that a bike helmet is there to protect against a concussion. That's not true.'

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In the lab, tests showed that helmets with air bags can dramatically reduce acceleration, which can lead to more severe injuries.

They claim that inflatable helmets are up to six times more effective than the foam alternatives.

Commercially available airbags for cyclists have been available for years and consist of a collar worn around the neck that contains the inflatable device.

HOW THEY WORK

Inflatable cycle helmets borrow their concept from the airbags used in cars.

The airbag itself is rolled up inside a collar along with a canister of compressed air.

A computer inside the collar uses an algorithm and motion detectors to work out when a cyclist moves in a sudden and unusual way that indicates an accident.

The airbag is then inflated within a fraction of a second so that it envelopes the rider's head.

Algorithms in the collar detect when a cyclist has a fall and deploys the airbag in a fraction of a second so that it envelopes the head.

Swedish manufacturer Hövding is one of those manufacturing airbag helmets for cyclists. They are, however, far more expensive than traditional bike helmets, costing around £219 ($279) each.

U.S. regulations do not reflect new research on the dangers of concussions and other brain injuries, Camarillo said.

The Consumer Product Safety Commission, which regulates bicycle helmets, does not even have a testing method in place for inflatable versions, he added.

As a result, he does not expect U.S. laws governing bicycle helmets to change any time soon.

Researchers have found that inflatable crash helmets (pictured) can reduce the impact of a head on the ground by up to six times compared to traditional foam based helmets. The tests used a model head that was dropped from a height of two meters to test impacts

Many cyclists ride without helmets altogether because they find them sweaty or hot. There are also some concerns they can make cyclists take more risks when riding. Inflatable airbags, contained within collars worn around the neck (as pictured above) could overcome this

Once the airbag has been deployed it needs to be replaced, much like traditional helmets after a crash.

Testing carried out by the company in 2014 showed the devices are three times safer than traditional head protection alone.

'We conducted drop tests, which are typical federal tests to assess bicycle helmets,' explained Mehmet Kurt, one of the team at Stanford putting the helmets through their paces.

'We found that airbag helmets, with the right initial pressure, can reduce head accelerations five to six times compared to a traditional bicycle helmet.'

The researchers used drop tests from a height of two meters (pictured), which are typical federal tests to assess bicycle helmets

Using dummy heads with accelerometers to measure the forces involved, the team dropped heads from a number of heights onto a solid platform – the equivalent of someone going full over the handlebars and onto their head.

The findings are published in the journal Annals of Biomedical Engineering.

'As our paper suggests, although air bag helmets have the potential to reduce the acceleration levels that you experience during a bicycle accident, it also suggests that the initial pressure that your air bag helmet has is very critical in reducing these acceleration levels,' said Dr Kurt.

Tests by Hövding (pictured), who make inflatable helmets, have suggested they can be three times safer than traditional helmets, but the new research suggests the airbag based devices may be even better than that

If the airbag is not fully inflated, the team claims it could cause the head to hit the ground with more force than if the rider wore a standard foam helmet.

They add that the airbag approach could potentially protect against concussions – which is thought to be a result of the brain tissue contorting rapidly inside the head on impact, stretching the neurons – paving the way for the use of such helmets around the world to protect cyclists.

'If our research and that of others begins to provide more and more evidence that this air bag approach might be significantly more effective, there will be some major challenges in the US to legally have a device available to the public,' added Dr Camarillo.